Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an "arrhythmogenic site" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart or in the pulmonary veins. The heart includes a number of normal pathways which are responsible for the propagation of electrical signals from the upper to the lower chambers necessary for performing normal systole and diastole function. The presence of arrhythnogenic site or accessory pathway can bypass or short circuit the normal pathway, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythnogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to the exact site for ablation. Once at the site, it is important for a physician to view the surrounding environment through the X-ray having contrast media and control the emission of energy to ablate the tissue within the heart or in the pulmonary veins.
Of particular interest to the present invention are radiofrequency (RF) ablation techniques which have been proven to be highly effective in tachycardia treatment while exposing a patient to minimal side effects and risks. RF catheter ablation is generally performed after conducting an initial mapping study where the locations of the arrhythmogenic site and/or accessory pathway are determined by the assistance of x-ray having contrast media. After a mapping study an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the ablation tip electrode lies exactly at the target tissue site. RF energy or other suitable energy is then applied through the tip electrode to the cardiac tissue in order to ablate the tissue of arrhythmogenic site, the accessory pathway, or the focal atrial fibrillation. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated.
Atrial fibrillation is believed to be the result of the simultaneous occurrence of multiple wavelets of functional re-entry of electrical impulses within the atria, resulting in a condition in which the transmission of electrical activity becomes so disorganized that the atria contracts irregularly. Once considered a benign disorder, AFib now is widely recognized as the cause of significant morbidity and mortality. The most dangerous outcome from AFib is thromboembolism and stroke risk, the latter due to the chaotic contractions of the atria causing blood to pool. This in turn can lead to clot formation and the potential for an embolic stroke. According to data from the American Heart Association, about 75,000 strokes per year are AFib-related.
A catheter utilized in the endocardial RF ablation is inserted into a major vein or artery, usually in the neck or groin area For focal AFib indications, a catheter is approached from the atrium to the ostium of a pulmonary vein. The tip section of a catheter is referred to hereby as the portion of that catheter shaft containing the electrode means which may be deflectable. The electrode means is to be positioned against the ostium of the pulmonary vein or inside the vein, whereby the electrode means having a firm wire, a ring electrode, an orthogonal electrode, a cap electrode, a guidewire, a mesh, or coil electrode means for lesion ablation.
The impedance usually rises at the tissue contact site when RF energy is delivered through an electrode. To create a deeper and larger controlled lesion, the surface of the tissue contact sites is preferred to maintain a proper temperature by a cooled fluid irrigation means to partially compensate for the temperature rise due to RF energy delivery.
The following U.S. patents have disclosed use of plurality of irrigation ports in different manners to cool the tissue contact surface. In practice, the fluid coming out of the irrigation ports may not evenly cover all the surface area of the electrode or the tissue to be ablated. Those patents are U.S. Pat No. 5,796,846 to Edwards et al., U.S. Pat No. 5,643,197 to Brucker et al., U.S. Pat No. 5,545,161 to Imran, U.S. Pat. No. 5,462,521 to Brucker et al., U.S. Pat. No. 5,437,662 to Nardella, U.S. Pat. No. 5,423,811 to Imram et al., U.S. Pat No. 5,409,000 to Imram, U.S. Pat. No. 5,348,554 to Imran et al., U.S. Pat No. 5,334,193 to Nardella, and U.S. Pat No. 5,313,943 to Houser et al. However, none of the above-referred patents discloses an irrigation system of fluid through a liquid-permeable means to control the fluid effusion through a combination of the distal end and/or through the sides of the distal section.
The tip section of a catheter is referred to hereby as the portion of that catheter shaft containing at least one electrode. In one embodiment, a catheter utilized in the endocardial RF ablation is inserted into a major vein or artery, usually in the neck or groin area. The catheter is then guided into an appropriate chamber of the heart by appropriate manipulation through the vein or artery. The tip of a catheter must be manipulatable by a physician from the proximal end of the catheter, so that the electrodes at the tip section can be positioned against the tissue site to be ablated. The catheter must have a great deal of flexibility in order to follow the pathway of major blood vessels into the heart. It must permit user manipulation of the tip even when the catheter body is in a curved and/or twisted configuration. The tip section of a conventional electrophysiology catheter that is deflectable usually contains one large electrode about 4 nmm in length for ablation purpose. The lesion is generally not deep because of potential impedance rise of tissue in contact with the catheter electrode and the ablation time needs to be cut short. Even in the case of a conventional catheter with irrigation capabilities by utilizing a plurality of irrigation ports, the cooled fluid do not evenly and uniformly rinse the ablation electrodes.
The fluid irrigation means may also include delivery of contrast media to view the local tissue configuration with assistance of X-ray imaging. The prior art does not teach methods for controlling contrast media effusion from the distal end for viewing the forward tissue conduit, or from the sides of the shaft distal portion for viewing the relative location of the device inside a conduit, and/or a combination of contrast venting to see the whole environment. Therefore there is a need for a new and improved catheter for viewing the device and tissue configuration inside a conduit by fluid irrigation means including appropriate fluid control means.